Feature request: nCr as nPr

themadmathematician shared this idea 10 years ago
Under Consideration

I just noticed that even though the command nPr is defined, nCr isn't. nPr[a,b] determines the number of permutations of b elements amongst a elements so nPr[4,2] is 12 because the first element can be taken in four ways and the second in three ways. Here, order matters.


nCr[4,2] = 6. This is the number of combinations of 2 elements amongst 4, where order doesn't matter. In other words, how many possible different groups of two persons can you get by subdividing a group of 4 different times.


Those calculators/software systems that have one of these functions normally also has the other one. On calculators it is normally an infix operator, being used as in 4 nCr 2 = 6.


My suggestion is that nCr is implemented since nPr is implemented already. Once done for GG5 it could perhaps be backported to 4.2 but there is no need to upset the release of 4.2 over this detail.

Comments (3)

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Ah - Slightly counter-intuitive... not much chance for a doubling of command names I guess. In Sweden students do permutations and combinations before they do binomial coefficients...

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Same in Finland. As calculator basically ALL use nCr, this is not a good move by geogebra.

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